Project summary Noise-induced auditory nerve loss (synaptopathy) has recently been identified as a form of hearing loss that may be widespread among humans. In this synaptopathy, moderate noise exposure results in the degeneration of auditory nerve synapses without hair cell loss or elevated auditory thresholds. This type of hearing loss cannot be detected by hearing tests conventionally used in the clinic, thus it has been termed ?hidden hearing loss?. This loss of auditory input may lead to degraded processing of sounds in the auditory cortex, particularly in the presence of background noise. In particular, synaptopathy may explain why 10% of the general population experiences difficulty understanding speech in noisy environments despite normal audiometric thresholds. To develop diagnostic and treatment strategies that address difficulty understanding speech in noise, there is a critical need to characterize the specific perceptual and central processing deficits resulting from synaptopathy. Since the Mongolian gerbil has a hearing range similar to that of humans, it is a well-established species for studying the physiological and perceptual consequences of hearing loss. This study uses the Mongolian gerbil to generate an animal model of synaptopathy more relevant to the range of human hearing than previous animal studies. Aim 1 identifies the appropriate noise exposure parameters for inducing synaptopathy in gerbil. Aim 2 tests whether synaptopathy results in poorer detection of amplitude modulations in the presence of background noise. Aim 3 tests whether synaptopathy results in degraded cortical representation of amplitude modulations and speech when background noise is present. Understanding the consequences of cochlear synaptopathy on central auditory processing and auditory perception is significant because this knowledge will help establish whether cochlear synaptopathy is a clinically- relevant problem. Furthermore, the animal model and techniques developed in this study can be used to study other deficits that may be associated with synaptopathy (e.g., hyperacusis and tinnitus) and evaluate the efficacy of strategies for diagnosing and treating synaptopathy. This study represents a significant step towards the long term goal of understanding how hearing loss affects central auditory processing and auditory perception.